As explained in aforesaid copending application, in the transfer of heat from a heat source to a heat-absorbing body, it is often desirable or even necessary in certain applications to employ an intermediary metallic member having a temperature coefficient of expansion approximately equal to that of the heat source but a relatively high heat-transfer characteristic. As explained in such copending application, such a heat-transmitting metallic plate unit has particular utility in the mounting of single-crystal silicon semiconductor devices.
The heat-transmitting metallic plate unit specifically described in aforesaid copending application comprised a plate of high-tensile-strength metal having a desirable coefficient of thermal expansion but undesirably low coefficient of heat transfer fabricated by filling holes in the plate with a malleable metal having a high coefficient of heat transfer such as copper, silver, aluminum, gold, or alloys of such metals. The holes were filled by electroplating, passing the metals through a rolling mill to force the malleable material into the holes, pouring the molten malleable metal into the holes, or by other means.
Such composite structure has the desired characteristics of controlled coefficient of thermal expansion and relatively high coefficient of heat transfer. It has found many applications where the range of temperature over which the device in which the structure is incorporated is relatively moderate, for example extending to a maximum temperature cycling range of the order of 400.degree. C. However, when operation over a higher range of cycling temperatures is required, it has been found that a small percentage of the malleable metal inserts become detached from the high-tensile-strength matrix material. As a result of the loss of contact between the two metals, the coefficient of heat transfer becomes degraded.
It is an object of the invention, therefore, to provide a new and improved prefabricated composite heat-transmitting metallic plate unit which overcomes the foregoing temperature limitation characteristic of the metallic plate unit described and claimed in aforesaid copending application and operates satisfactorily over a higher range of cycling temperatures, for example 550.degree. C.